Easing
Defalut is lenear.
There are some easings in below table. You can use these strings.

In

Out

InOut

OutIn

Sine

easeInSine

easeOutSine

easeInOutSine

easeOutInSine

Quad

easeInQuad

easeOutQuad

easeInOutQuad

easeOutInQuad

Cubic

easeInCubic

easeOutCubic

easeInOutCubic

easeOutInCubic

Quart

easeInQuart

easeOutQuart

easeInOutQuart

easeOutInQuart

Quint

easeInQuint

easeOutQuint

easeInOutQuint

easeOutInQuint

Expo

easeInExpo

easeOutExpo

easeInOutExpo

easeOutInExpo

Circ

easeInCirc

easeOutCirc

easeInOutCirc

easeOutInCirc

You can set these strings with uppercase or lowercase.
easeinsine, EASEINSINE, easeInsine are also OK.

$('#options3').ratween({left:'400px'},{easing:'easeInQuint'});

click

Caution!
I made these easings thinking about Tweener.easing.
But actually this plugin's easings and Tweener's those are not completely equal. These are nearly equal.
Because I used cubic curve-bezier to simulate easing expression. (see this site)
Cubic bezier curve can't simulate easing expression completely.
So if you change easing curve, try to change the curve value in source code.

Callback
It is triggered when transition is complete. Defalut is nothing.